1. Field of the Invention
The present invention relates to a conversion circuit that eliminates the undesirable phase shift of the R-Y (or "V") chrominance component relative to the B-Y (or "U") chrominance component of a phase-alternating line format video signal, as characteristic of a PAL video signal, by replacing the signal on every other line with the signal from the previous line, to thereby generate a chrominance signal with R-Y and B-Y axes referenced at unalternating phase, as in an NTSC (National Television System Committee) chrominance composite signal.
2. Prior Art
NTSC television or video signals include a horizontal sync pulse followed by a color burst which in turn is followed by a chrominance/luminance signal in each scanning line. The chrominance and luminance signal contains the information for displaying a color picture. NTSC signals include 525 lines per frame, which is composed of two fields. There are 60 fields per second. The NTSC signal has quadrature modulated chrominance referenced to a phase as defined by the burst.
The PAL composite signal also has quadrature modulated chrominance, however one axis (R-Y or "V") is inverted on alternating lines. Hence the term "phase alternating line" signals. Additionally, PAL signals have 625 lines per frame and 50 fields per second or 25 frames per second.
The NTSC standard was the first color television system and was originally introduced in the United States. Generally, it is used in the U.S., Japan, Canada and Mexico. The PAL system was developed in Europe and is generally used in the United Kingdom, Australia and some other European countries. Video tapes made using phase alternating chrominance signals cannot be played by VCRs (video cassette recorders/players) and shown on displays capable of decoding only unalternating phase signals, unless the foregoing difference in line-by-line axis inversion is resolved.